Solid state electronic watch

ABSTRACT

A watch is provided with a liquid crystal display system operable at high levels of ambient illumination and a solid state display system operable at low levels of ambient illumination. A photo-transistor selects the display system appropriate to the ambient light level.

United States Patent Mltsul 51 June 13, 1972 [5 SOLID STATE ELECTRONICWATCH [56] Relerences Cited [72] inventor: l-liromitsu Mitsui, Nagano,Japan NI E STATE P TENT [73] Assignee: Kabushlki Kaisha Suwa sgik h T k3,505,804 4/ I970 Hofstein ..58/23 R Ja an 3.5 l6,242 6/l970 Leh0vec....58/23 R 3,576,099 4/!971 Walton 11.58/23 R [221 1971 3,613,351 10/1971Walton ..58/23 [2]] Appl. No.: 197,378

Primary ExaminerStephen J. Tomsky Assistant Examiner-Edith C. SimmonsJackmon Attorney-Alex Friedman, et al. Foreign Application Priority Data[57] ABSTRACT A watch is provided with a liquid crystal display systemopera- N 1 0V I970 Japan As/[00709 ble at high levels of ambientillumination and a solid state display system operable at low levels ofambient illumination. A [52] US. Cl. ..58/ R, 350/l R pholodransistorSelccs the display system appropriate to the [51] Int. Cl .G04b 19/30,H03k 19/14 ambient gm IevcL [58] Field oiSearch ..58/23, 50; 350/ 10Claims, 4 Drawing Figures PATENTEDJun 13 I972 SHEET 10F 2 FIG./

F/GZZ BACKGROUND OF THE INVENTION Liquid crystal display devices dependupon the fact that the imposition of a sufficient electric field on aliquid crystal material causes the liquid crystal material to disperselight and thus to appear to be luminous. However, the light to bedispersed must be provided from outside the device. Consequently, eventhough the amount of electrical energy required is very small, such adevice is unsuitable for use where the level of ambient illumination islow.

In contrat, electroluminescent, i.e., self-luminous devices such asthose based on gallium-arsenide require substantially greater amounts ofenergy since the temperature of the display element must be increased.Also the heat produced must be rejected to the exterior of the device.When an attempt is made to use such a device in regions of high ambientillumination, a high level of luminescence is required for the lightproduced to be perceptible, resulting in a considerable energy drainfrom the energy source.

SUMMARY OF THE INVENTION Incorporated in a watch are a liquid crystaldisplay device and a self-luminous display device. The former is apassive device and is suitable for use at high ambient light levels. Thelatter is an active device and utilizes an electrically poweredself'luminous solid state material such as gallium-arsenide; it issuitable for use at low ambient light levels or in complete darkness. Inthis device, a photo-transistor senses the ambient light level, and, inaccordance with the light level, either im poses an electric field onthe liquid crystal material or powers the self-luminous solid statematerial. In order to decrease the total energy consumed, thephoto-transistor, its associated circuitry and the selected displaydevice are energized only when the user wishes to note the time.

Accordingly, an object of the present invention is to provide animproved watch having an electrically powered display system suitablefor use at all levels of illumination, including total darkness.

Another object of the invention is to provide an improved electricallypowered display system comprising a liquid crystal material for use athigh levels of illumination and a solid state self-luminous material forlow levels of illumination.

A further object of the invention is to provide an improved electricallypowered display system incorporating a device for determining the levelof illumination and selecting an appropriate display means.

Yet another object of the invention is to provide an improvedelectrically powered display system which functions only when energizedby an exterior signal.

Still other objects and advantages of the invention will in part beobvious and will in part be apparent from the specification.

The invention accordingly comprises an article of manufacture possessingthe features, properties, and the relation of elements which will beexemplified in the article hereinafter described, and the scope of theinvention will be indicated in the claims.

BRIEF DESCRIPTION OF THE DRAWING For a fuller understanding of theinvention, reference is had to the following description taken inconnection with the accompanying drawing, in which:

FIG. I is a plan view of an electrically powered digital display systemconstructed in accordance with a preferred embodiment of the presentinvention;

FIG. 2 is a cross-sectional elevational view of the device of FIG. 1;

FIG. 3 is a sectional view at an enlarged scale, taken along line 3-3 ofFIG. 1; and

FIG. 4 shows schematically the arrangement of the components of thedisplay device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A solid state electronic watchin accordance with the present invention is generally indicated by thereference numeral I0. The watch has a transparent base plate II. Thedisplay portion of the watch is made up of segments 12; in theembodiment shown in FIG. 1 each of the indicia has seven segments.Phototransistor I3 which is responsive to incident light controls adivider, oscillation and driving circuit and crystal vibrator portion14, using an MOS (metal oxidesemiconductor) transistor. Day and datedisplay elements 15 and 16 are preferably mechanically activated. In apreferred form, the day and the date are printed on planar, ring-shapeddisks which are advanced once a day by means of electric plungers, forinstance; it is not uneconomical of electrical energy to advance thesedisks in this way because the electromechanical activation elements needbe energized only for a short time.

While the advancement of the day and date disks l5 and 16 occursautomatically, the time display consisting of the segments I2 isactivated only on pressing a switch 17. The selection of the displaymode is, of course, controlled by the phototransistor 13, but the levelof incident light at which the choice changes can be set manually. Thisadjustment is not shown. Similarly, the current fed to self-luminouselement 18 (FIG. 2) may also be adjusted by means not shown.

A cell for holding liquid crystal material is formed by spacers 2]between cover 22 and transparent base plate I]. Liquid crystal material19 normally is transparent, but when a sufficiently high voltagetransverse to the cell is impressed between appropriate segments 12 andtransparent base plate 1 I, a desired numeral becomes visible by reasonof dispersion of incident light from the surroundings. It should benoted that the brighter the incident light, the more light is dispersed,and consequently the brighter the indicia appear. Consequently,indication of the time by this method is eminently satisfactory wherethe level ofillumination is high.

Where the level of illumination is low, or where illumination iscompletely absent, photo-transistor 13 passes current throughappropriate display elements of gallium-arsenide crystal I8. As isevident, the lower the level of the ambient illumination, the morestrongly will the self-luminous display elements appear.

Another embodiment is shown in FIG. 3 wherein a galliumarsenide displayelement, an MOS transistor and a liquid crystal cell are mountedmonolithically on one semi-conductor base plate 23. Base plate 23consisting of a sapphire or a spinel is separated from cover 22 bysealing layer 24. Electrode 25 is provided for driving liquid crystal I9into the dispersion state. Self-luminous element 26 of gallium-arsenideis mounted on semi-conductor base plate 23. Display cell 27 is soarranged that each desired segment is illuminated from the rear byinfra-red radiation emitted by electroluminescent element 26. By usingthe liquid crystal material in combination with the infra-red radiatingself-luminous material, visible light is produced and the powerrequirement is very low. Where the available space is small as is thecase with a watch, it is desira ble that the self-luminous displayelement and the liquid crystal element be combined, but if desired, theymay be arranged separately, or one may overlie the other in part only.

The arrangement of the electrical components of the system is shown inthe electrical block diagram of FIG. 4 wherein the signal of crystaloscillator 29 which constitutes the time standard for the system isdivided by divider 31 which employs an MOS transistor. The output fromdivider circuit 31 is supplied to driving circuit 32 from which energyis then transferred either to liquid crystal system 33 or self-luminoussystem 34, The selection is made by the photo-transistor circuit 28.Since the energy expended in operating liquid crystal display system 33is in the range of microwatts, this display system is termed passive."The self-luminous display system 34 consumes energy in the range ofmilliwatts and is therefore termed active." Where the base plate 23 isof semi-conductor material as shown in FIG. 3, then the photo-transistor13 may be mounted in the base plate.

Although the day and the date displays are more conveniently mounted onseparate wheels, they are shown as one wheel 35 in FIG. 3. If desired,however, the day and the date may also be presented by means of displayelements similar to those used for indicating time. Such an arrangementis shown diagrammatically in FIG. 4 by boxes 36 and 37.

It will thus be seen that a novel solid state electronic watch of highreliability is provided in which the time can be shown with an extremelysmall expenditure of energy. Consequently, such a watch will operate forextended periods of time between replacements of a driving battery. Bymeans of the system described, time is displayed where the level ofillumination is high with virtually no expenditure of energy, and wherethe level of illumination is low, at very low expenditure of energy.Operation by these alternate means is made possible by the use of aphoto-transistor with associated circuitry, so adjusted that the methodof display is changed at a selected level of illumination.

It will thus be seen that the objects set forth above, among those madeapparent from the preceding description, are efficiently attained and,since certain changes may be made in the above article without departingfrom the spirit and scope of the invention, it is intended that allmatter contained in the above description and shown in the accompanyingdrawing shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention hereindescribed, and all statements of the scope of the invention which, as amatter of language, might be said to fall therebetween.

What is claimed is:

l. A solid state electronic watch comprising a passive display elementfor time display in regions of relatively high incident light intensity,an active display element for time dis play in regions of relatively lowlight intensity and means for activating said passive and active displayelements.

2. A solid state electronic watch as defined in claim 1,

wherein said passive display element includes a sealed cell having atransparent outer face and liquid crystal material within said cell andsaid activating means includes means for imposing a voltage transverseto said cell sufficient to cause said liquid crystal material todisperse light.

3. A solid state electronic watch as defined in claim 2, wherein saidouter face has thereon segments in an array such that any digit from 0to 9 may be shown by suitable activation by said activation means.

4. A solid state electronic watch as defined in claim 1, wherein saidactive display element includes an electroluminescent materialactivatable by said activation means to emit radiation, said activationresulting from passage of current through said electroluminescentmaterial.

5. A solid state electronic watch as defined in claim 3, wherein saidactive display element has thereon segments in an array such that anydigit from 0 to 9 may be shown by suitable activation by said activationmeans.

6. A solid state electronic watch as defined in claim I, wherein saidactivation means comprises a photoaransistor positioned in said watch tosense the level of said incident light and generate a signalcharacteristic of said incident light level, and circuit means toactivate said passive display element at high incident light levels andto activate said active display element at low incident light levels.

7. A solid state electronic watch as defined in claim 1, wherein saidactive display element is disposed behind said passive display elementso that said active display element, when activated, may be viewedthrough said passive display element.

8. A solid state electronic watch as defined in claim 6, wherein aportion of said active display element overlies a portion of saidpassive display element.

9. A solid state electronic watch as defined in claim I,

wherein said watch includes a semi-conductor base plate and said displayelements and said activating means are mounted monolithically on saidbase plate.

10. A solid state electronic watch as defined in claim 3, wherein saidelectroluminescent material is gallium arsenide.

1. A solid state electronic watch comprising a passive display elementfor time display in regions of relatively high incident light intensity,an active display element for time display in regions of relatively lowlight intensity and means for activating said passive and active displayelements.
 2. A solid state electronic watch as defined in claim 1,wherein said passive display element includes a sealed cell having atransparent outer face and liquid crystal material within said cell andsaid activating means includes means for imposing a voltage transverseto said cell sufficient to cause said liquid crystal material todisperse light.
 3. A solid state electronic watch as defined in claim 2,wherein said outer face has thereon segments in an array such that anydigit from 0 to 9 may be shown by suitable activation by said activationmeans.
 4. A solid state electronic watch as defined in claim 1, whereinsaid active display element includes an electroluminescent materialactivatable by said activation means to emit radiation, said activationresulting from passage of current through said electroluminescentmaterial.
 5. A solid state electronic watch as defined in claim 3,wherein said active display element has thereon segments in an arraysuch that any digit from 0 to 9 may be shown by suitable actIvation bysaid activation means.
 6. A solid state electronic watch as defined inclaim 1, wherein said activation means comprises a photo-transistorpositioned in said watch to sense the level of said incident light andgenerate a signal characteristic of said incident light level, andcircuit means to activate said passive display element at high incidentlight levels and to activate said active display element at low incidentlight levels.
 7. A solid state electronic watch as defined in claim 1,wherein said active display element is disposed behind said passivedisplay element so that said active display element, when activated, maybe viewed through said passive display element.
 8. A solid stateelectronic watch as defined in claim 6, wherein a portion of said activedisplay element overlies a portion of said passive display element.
 9. Asolid state electronic watch as defined in claim 1, wherein said watchincludes a semi-conductor base plate and said display elements and saidactivating means are mounted monolithically on said base plate.
 10. Asolid state electronic watch as defined in claim 3, wherein saidelectroluminescent material is gallium arsenide.